Before I dig in, understand that these are generalizations. You can always find exceptions. An experienced, local travel agent can help you make sense of which option can be a better fit for your next trip!
Cruise - When you are on a cruise, you are on a "floating hotel". If you pull into a port and don't like it....don't worry! Tomorrow you'll be in a new port. Part of the appeal of cruising is that you can unpack once, and then see multiple locations throughout your sailing. You traditionally only have between six and ten hours in port. One thing to remember is that you are on the ship's schedule, so it can be more difficult to move at your own pace when you know you have to get back to the ship at a certain time. This all being said, All-Inclusive resorts tend to be confined to Mexico, the Caribbean, and Latin America. Cruises go everywhere. All the continents. including the South Pole!
Cruise - Be prepared for a smaller space when setting sail on a cruise. Cruises can have over twenty different options for cabin categories. When you see pricing for cruises advertised, it is almost always going to be interior pricing. This means there are no windows or access to a balcony. Traditionally, interior cabins will be the cheapest, with costs going up for an oceanview (window), or balcony cabin. Regardless of the category, the spaces tend to be smaller than a standard hotel room, with beds that either are separate twins, or can be pushed together for a king. With more than two people in the cabin, there will be additional options for sleeping. This might be a pull down bunk bed. Or even a pull-out couch. Bathrooms on cruises are compact. Many times there is only a shower, no tub. There is usually a desk, mini-fridge, and small television.
Cruise - Cruises also have a schedule that lists what activities take place each day. Typically, each evening during turndown service a steward will place the following day's schedule in your cabin. There may also be boards posted around the ship with activity options for that day. The range of activities is similar to all-inclusives. Something to remember is that for the most part, cruise ships have casinos in them. Certain locations don't allow for casinos at all-inclusives.
Cruise - The food situation on a cruise is unique if anything. For one thing, you are usually asked when making your reservation if you want to eat "early" or "late". This is in reference to dinner, and early is usually around 6pm and late is around 8pm. In recent years, cruises are also allowing "anytime" dining, where you can eat anytime you wish. Cruise lines like Norwegian are considered "freestyle", where they don't even have an early or late option.
For other options, there are always going to be big buffets on cruises. And there are also sit-down restaurants. Beweare that these sit-down restaurants can cost extra. There are also snack bars by pools, and room-service to meet your needs.
Cruise - The only beverages that come standard on cruise ships are water, lemonade, juice, coffee, milk, and tea. Higher end coffee drinks, soda, and all alcohol cost money. Most cruise lines have beverage packages you can buy. Expect to pay around $50 per person per day. On top of this, there is usually a 15% gratuity added on for each purchase. This all being said, the drinks on cruise ships can be stronger than at resorts. And if you befriend a bartender or server on one of your first days and give a good tip, they can take very good care of you.